1. Field of the Invention
The present invention relates to a LED (light-emitting diode) phosphor and fabricating method thereof, and particularly relates to a LED phosphor having a light-emitting thin film (or photoluminescence thin film) made of an organic material and a zinc oxide microstructure (or nanostructure), a method for fabricating this LED phosphor by hydrothermal method and combination of the organic material and the zinc oxide microstructure (or nanostructure), and a method of photoluminescence employing this LED phosphor to emit white light.
2. Description of Related Art
As the requirement of energy saving and environmental consciousness are increased, the white light emitting diode (white LED) is employed instead of the conventional white light bulb and tube gradually. Now, the white LED is fabricated by following three methods: (1) A multi-chip LED or RGB LED is formed by combining a red LED, a green LED and a blue LED. The multi-chip LED (or RGB LED) emits white light by mixing the red light emitted from the red LED, the green light emitted from the green LED, and the blue light emitted from the blue LED. (2) A blue LED is used to emit a blue light. The yellow phosphor, such as YAG(Y3Al5O2), coated on a epoxy resin is excited by a portion of the blue light to emit a yellow light. Another portion of the blue is mixed with the yellow light to emit a white light. (3) A purple LED is used to excite a red phosphor, a green phosphor, and a blue phosphor to emit a red light, a green light, and a blue light respectively. The red light, the green light, and the blue light are mixed to generate a white light.
However, all of the foregoing methods have shortcomings. In the method (1), it has a need of different driving circuits to drive different LED chips because the RGB LED is composed of different LED chips. The process of fabricating the RGB LED becomes complicated due to these driving circuits, and the multi-chip LED (or RGB LED) has bad heat dissipation. Therefore, the method (1) has disadvantages of complicated fabricating process and bad heat dissipation.
In the method (2), most raw materials of the phosphor are rare earth elements. The yield of rare earth elements is few and it is difficult to mine the rare earth elements. Thus, the prices of the rare earth elements are high and still rising, and the costs of the phosphor and the white LED are increasing. Furthermore, the surface vegetation of the earth is broken when rare earth elements are mined. It results in a serious environmental disruption. The phosphor is usually fabricated by solid-state sintering. In the solid-state sintering process, the raw material of the phosphor need to be sintered at the temperature over 1000° C. for a long period of time, and thus the cost of fabricating the phosphor is increased. Therefore, the method (2) has disadvantages of increasing cost and environmental disruption caused by employing the rare earth elements and the solid-state sintering.
Similar to the method (2), the method (3) also has disadvantages of increasing cost and environmental disruption because it has a need of employing the red phosphor, the green phosphor, and the blue phosphor in the method (3). Furthermore, the method (3) has another disadvantage that it is difficult to mix the red phosphor, the green phosphor, and the blue phosphor with each other. Generally, the process of the method (1) is too complicated so that most of the present white LEDs are fabricated by the methods (2) and (3). Therefore, the phosphor is indispensable to the white LED. Accordingly, the problems of high production cost of the white LED caused by the phosphor and the environmental disruption caused by mining the rare earth elements cannot be resolved.
Therefore, it has a need of a fabricating method of a LED (light-emitting diode) phosphor. In this method, other material, which is cheap, easy to be obtained, and environmentally friendly, is used instead of the rare earth elements to be the raw material of the phosphor, and the phosphor is fabricated with simple process, simple processing conditions (or requirements) and low cost. Moreover, the cost of producing a white LED can be decreased and the process of producing a white LED can be simplified by employing this phosphor to produce a white LED.